beta particle

A fast-moving electron or
positron (anti-electron) that is emitted
from a nucleus during the radioactive
process known as beta decay. Large amounts
of beta radiation may cause skin burns, and beta emitters are harmful if
they enter the body. Beta particles may be stopped by thin sheets of metal
or plastic (see absorber).

Most neutron-rich or neutron-deficient atoms that are lighter than lead
decay by beta decay. What happens is that a neutron
changes into a proton or vice versa. In the
transformation n
p the nucleus loses a negative charge and emits an electron, e-.
In the transformation p
n the nucleus loses a positive charge and emits a positron, e+.
For example, 14-C
14-N + e- or 18-F
18-O + e+.

Beta particles travel with an initial speed of about 180 million m/s, or
about 0.6 light-speed. Because they are
charged they will interact with electrons in atoms they come close to and
cause ionization. A medium energy beta
particle will travel about one meter in air but only about one millimeter
through body tissue.

Energy distribution of electrons (beta-particles)
emitted during the beta decay of P-32. Credit: European Nuclear Society

Beta radiation has an energy continuum. The maximum energy
Eβmax is always quoted, e.g. for P-32 decay this is 1.7
MeV (see graph). Beta rays span an energy range of 0.003–13 MeV, and
their distribution is characteristic of the emitting isotope.

Beta particles were discovered by Henri Becquerel
in 1876, although at that time their nature was not understood.